Air seeders typically include an implement frame mounted on wheels, with a plurality of furrow openers mounted on the frame. The furrow openers can be moved from a raised non-operative position to a lowered operating position where the furrow openers engage the ground and create furrows. Agricultural products such as seed and various types of fertilizer are carried in separate tanks which can be mounted on the implement frame or on a cart towed along with the implement frame.
Metering devices dispense products from the tanks into one or more air streams that carry the products through a network of hoses and manifolds to the furrow openers where same are deposited in the furrows. In order to achieve a uniform application rate of agricultural products on the field, the rate of product flowing from each output port of each manifold to each furrow opener should be the same.
In a typical configuration, the manifold is a short cylindrical shape and is mounted on top of a vertical tower section of the input conduit. The input port is at the center of the bottom plate of the manifold, and the output ports are equally spaced around the cylindrical wall of the manifold between top and bottom plates. The number of output ports will vary with the particular application.
In order to achieve substantially equal division of the agricultural products entrained in the air stream, it is desirable to have the products randomly distributed across the cross-section of the input conduit as it enters the manifold input port. Since the air stream entering the manifold moves more or less equally out of the manifold through each output port, an imbalance in the amount of product in one part of the air stream compared to another will result in a similar imbalance in the quantity of agricultural products carried out through one output port compared to another.
The vertical tower section helps to move the suspended product into a more even or centered distribution across the cross section of the tower portion of the input conduit. The bottom end of the tower section is connected through a curved elbow to a horizontal section of the input conduit. In the horizontal section the agricultural products tend to move toward the bottom side of the conduit in response to gravity, and the vertical tower section is designed to take out the effects of gravity. As the air flow moves around the curve elbow at the bottom of the manifold system the product tends toward the outside of the curve giving an offset distribution of product, and various means are then used to shift the product to a random or centered distribution.
For example, U.S. Pat. No. 4,575,284 to Kelm provides projections or dimples extending inward from the wall of the vertical tower section to help the granular material reach the manifold input port in a centered, accurate stream. Canadian Patent Number 2,111,611 to Bourgault discloses a seed centering system comprising one or more tapered centering rings which direct the agricultural products away from the walls toward the center of the horizontal and vertical tower sections of the primary conduit.
A cone with curved walls commonly extends down from the top plate toward the input port to redirect the upwardly moving air stream and entrained product to exit horizontal through the output ports. U.S. Pat. No. 6,290,433 to Poncelet discloses a manifold where the input port gradually tapers inwardly in the direction of the flow to accelerate and centre the flow as it enters the manifold. Poncelet also discloses a manifold top plate or cap with a downward extending point centered on the central axis of the input port. A series of smoothly curved grooves and ridges extending from the point upward and curving 90 degrees to connect the grooves with the output ports. Corresponding grooves and ridges are provided in the bottom plate and the ridges in the top and bottom plates cooperate to essentially form substantially separate channels from an open area just above the input port near the point to each output port.
United States Published Patent Application Number 2015/0098767 to the present inventor Beaujot discloses a manifold where the air stream contacts a downward oriented cone in the top plate and is directed into channels extending downward along outer walls of the manifold and then curving to direct the air stream horizontally through the output ports.
The volume and speed of the air stream in the input conduit varies to accommodate the wide range of product flow rates that must be carried through the networks. This variable, and others such as the properties of the particular product being carried make obtaining an air stream with the product uniformly distributed across the cross-section of the input conduit problematic.
Further complicating the problem is the variability in the back pressure present in the hoses leading downstream from the output ports of the manifold, which causes air, and the products entrained therein, to flow more readily out the output ports with lower back pressure. For example the lengths of the hoses from each manifold output port can vary resulting in unequal back pressure, and positioning of manifolds and furrow opener locations may make it difficult achieve equal hose lengths. United States Published Patent Application Number 2014/0216315 of the present inventor Beaujot discloses a manifold where the size of the output ports is adjustable to balance the back pressure at each output port, however while balancing the back pressure substantially equalizes the amount of air moving out through each output port, where the product is not equally distributed through the air stream, unequal rates of product still flow from the output ports.